


Unlikely Invitation

by camichats



Category: Marvel
Genre: Accidental Voyeurism, Anal Sex, Established Tony Stark/Sharon Carter, Explicit Sexual Content, F/M, Getting Together, M/M, Masturbation, Multi, Pining, Polyamory, Polyamory Negotiations, Strap-Ons, Vaginal Sex
Language: English
Status: Completed
Published: 2019-03-05
Updated: 2019-03-05
Packaged: 2019-11-12 16:16:39
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,433
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/18014150
Author URL: https://archiveofourown.org/users/camichats/pseuds/camichats
Summary: It was bad enough to be pining after two people, but it just got worse when Steve found out that they were dating each other.





	Unlikely Invitation

**Author's Note:**

> Fill for kink bingo: Anal Sex

Steve had thought it was pretty safe to have a crush on the two people he liked. There was no way they knew each other, so he didn't have to worry about any drama there. Not that he really had _anything_ to worry about of course, because Tony wasn't interested in him, and Kate gave him a kind no the one time he'd asked her out.

Of course then that all went up in smoke because apparently there was a shit ton of information Steve didn't know. Like that Kate was actually Sharon, a Shield agent. Or like Tony was long since taken and all the rumors about him sleeping were just that: rumors. Or like the fact that Sharon and Tony knew each other? That one really threw him for a loop, and it was a weird as hell trick of the universe that they not only knew each other, but they were _dating_. Steve had thought of both of them as safe options for his affection, and while that was still true, it was for an entirely different reason than the one he thought.

"So," Steve said when they were all sitting around the kitchen table late one night after a mission, "how'd this happen?" He motioned between the two of them to convey what 'this' referred to. Normally Steve didn't like to pry, but when Sharon was easily moved from active Shield duty to being an Avenger and sharing a room with Tony like it was no big deal, he figured it wasn't a secret.

Tony shrugged, and Sharon did the same, giving him an apologetic look.

"You... don't know how you got together?" he asked, a large heaping of disbelief in his voice.

"It kinda happened one day," Tony said. "There wasn't a plan or a date, we were just suddenly together." He was eyeing the table like he was determining how comfortable of a pillow it would make.

Sharon smoothed a hand up his back and massaged his neck, which made him droop further towards the surface. She nodded along with what Tony said, her other hand holding onto her drink, rotating the glass to keep her fingers busy. "We sort of grew up in each other's back pocket. I held the title of best friend until Rhodey showed up, so I became the girlfriend and," she shrugged, "here we are."

"You are both girlfriend and best friend."

"Rhodey's your best friend. Or maybe Pepper."

"I have lots of best friends, and you are on the list. So are you, Stevie-bird."

"Bird?" he asked, ignoring the way his heart thumped a little louder in his chest at the confirmation that Tony thought of him as a good friend.

"Yeah I was trying it out." His forehead finally hit the surface of the table, and he closed his eyes. "Don't think I like it."

"C'mon Tony, let's get you to bed. Night, Steve." Sharon sent him a smile as she pried Tony off the table with minimal complaint, and he leaned against her as they walked to their room, his arm curved around her waist and hers around his shoulders.

Steve watched them leave, heart aching. "Goodnight," he whispered, pulling his cup closer as it was the only company he was going to get for the rest of the evening.

* * *

Steve was getting home early from a mission, and he was looking forward to taking a shower and having a nice long time to get himself off since he usually rushed himself in between running places, never truly taking the time to relax and enjoy it.

It had been a solo mission that was supposed to last six days but had only needed four and a half, so he didn't know what the rest of the team was up to. If there was a movie night going on he might join them, but the idea of locking himself in his room for a while sounded very appealing.

The elevator doors opened, and Steve stepped out, running a hand through his sweaty hair as the other kept his bag from falling off his shoulder. He was so wrapped up in thinking about his nice, warm room that he didn't hear what was happening in the living room until he could see it too.

The fireplace was going-- Steve hadn't known Tony ever used it but here they were-- and in front of it were Sharon and Tony, both of them naked and practically glowing in the firelight. Tony was on his knees, resting his weight on his elbows. Sharon was behind him, hands on his hips as she fucked him. Tony moaned loudly and pushed his hips back to meet her thrusts, and all of Steve's blood decided that it could go to either his cheeks or his dick. Sharon had tied her hair back, and the muscles in her stomach and arms were obvious as she moved.

Steve wished he could sneak off to his room without them noticing, but it was on the opposite side of where they were, and if he didn't say something now then he would have to tell them later. Actually that wasn't such a bad idea. He tore his eyes away and kept them trained on the floor as he edged around the room, doing his level best to ignore the sounds they were making-- gasps and groans and muttering the other person's name with praise and swears that made Steve _want_. He just wanted to get to his room without embarrassing any of them.

He was miraculously able to make it across the room undetected, but not quick enough to miss the way either of them sounded when they were coming. He swallowed hard and walked carefully the rest of the way to his room, making sure to be quiet with the door as he closed it. "Fuck," he muttered, closing his eyes as he banged his head back against the door, dropping his bag and working his pants open. He licked his hand before he wrapped it around his cock. It wasn't really enough, but it never took much for him to come and with what he'd just witnessed it was no time at all before he made a mess in his hand.

Neither Sharon nor Tony were the sort of people to take a risk on anyone walking in on them, which meant that they had been one hundred percent certain that they were alone in the Tower before they set themselves up in the living room.

Almost immediately, Steve felt a hot wash of shame go over him. It was one thing to think about them while he masturbated, it was quite another to intrude on a private moment and use that to get himself off. He shuffled off to the bathroom to clean up and mused that this would all be so much easier if he could just get over them, but every time he thought he might, he fell more in love.

Out in the living room, Sharon eased out of Tony carefully before flopping to the floor beside him.

"Fireside sex is a little too warm," Tony mumbled, but he made no move to get away from it or to turn the fireplace off.

"This was your idea."

"And I enjoyed it, but don't you think this is too warm?"

"It is." Neither of them moved.

* * *

Steve's plan was to say something to them in the morning at breakfast, or as near to breakfast as he could get if they decided to sleep in. He walked through the living room to the kitchen and was so determined to not look at where they'd been the night before that he missed the fact that there were still clothes strewn about. If he had looked, it would have given him some warning about what was about to happen.

He was innocently inspecting the differences between two cereals when they walked in. He'd heard them coming, bare feet and giggling conversation, but hadn't thought twice about it. They were happy and in love, this wasn't so strange. Except then he looked up to say good morning and the words caught in his throat. Sharon was wearing one of Steve's shirts. He'd thought he lost that shirt months ago so that was strange enough, but then he noticed that that was _all_ she was wearing. It was a big shirt on her, but not big enough to cover all her private bits. If that wasn't enough, Tony was wearing Captain America decorated boxers that were worn from age.

To put it simply, this was like the beginning of a Steve-centric porno. It wasn't a porn movie though, because if it was, Sharon would sit on the counter and pull the shirt up so that it hid even less, and Tony would be wearing a Captain America themed butt plug. Technically Steve didn't have proof that the second one wasn't true, but it seemed highly unlikely and even if it _was_ true, Tony wasn't going to show him. Or let him know. Which was a damned shame because Steve was liking that concept more and more.

The couple froze a few steps inside the room, and Sharon tugged on the front end of the shirt so it would cover her cunt. "Oh," Tony said, moving so he was partially in front of Sharon. His modesty was a boat long since sailed, so the least he could do was preserve hers a little. "Sorry Steve, we thought we had the place to ourselves."

Steve cleared his throat, blushing hard as he stared unseeing at the cereal boxes. "Clearly. You know Sharon, I thought I lost that shirt."

"It's comfortable," she said defensively, and Steve could see movement out of the corner of his eye that probably meant she was pulling on it some more.

"Does that mean I'm not getting it back?"

"I'm surprised you would want it back after this."

Steve was about to say that he was just teasing and she could keep it before he made an exit-- probably with both boxes of cereal, his bowl and spoon, and the gallon of milk-- but he paused as something occurred to him. Sharon and Tony were a couple. They were half-naked and walking around like that when they thought the Tower was empty. What clothes they _were_ wearing, were related to Steve. Why would they dress like that when they were surely planning on fooling around? "Why are you wearing those?" he asked, eyes darting quickly to Tony's boxers and then away again.

"Because otherwise I'd be naked? Look Cap, we're sorry about this. We'll just get out of your hair so you can eat breakfast in peace." They left before Steve could get to the heart of the matter, could ask them why the fuck they were going to have sex wearing things that were Steve's? Or, more accurately, felt like Steve was making a claim on the two of them?

Steve ate, read a little, went for a run, and was back in the kitchen for second breakfast when he saw them again. They both looked sated and happy, though fully clothed this time. He told himself very firmly that he was not disappointed.

Neither of them mentioned what happened earlier that morning, or what Steve might have seen from the night before. Steve sure as hell didn't want to be the one to bring it up, so they chatted like usual, ignoring the tangoing orange rhinoceros in the room.

This was fine.

* * *

The main problem was that Steve couldn't just forget what he'd seen. With Tony, he always imagined himself on top. Given that Sharon had been fucking him that night, Steve's fantasies were unchanged. He imagined himself on top with Sharon about half the time, but the other half had never included her pegging him... until now.

Steve was on his knees, fucking himself back on the toy, imagining Sharon's hands on his hips. The fantasy had started with her in that goddamn shirt-- which had been returned to him a few days ago, freshly cleaned and neatly folded on top of his bed-- before stripping out of it and taking him hard. Needless to say he was seeing stars, panting harshly as he lost himself in the fantasy and then coming hard, back bowing as he came in thick spurts over his sheets.

And of fucking _course_ that was when Tony walked in, giving a cursory knock on the door before trying the handle and opening it easily. It wasn't until Tony was gaping at him with wide eyes that Steve realized that he'd forgotten to lock the door, but that was too-little/too-late of a realization. A good time to remember that would have been literally any time before Tony walked in.

"Uh." Tony looked frozen to the spot, which was a good reason for Steve not to get mad at him, so if asked he would cite that. "I guess you're busy?"

Steve swallowed, wondering if it would be more or less awkward if he eased the toy out of himself right now. "Not anymore. I can talk in a minute if you'll just." He lifted a lethargic arm and made a spinning motion with his hand to convey that Tony should turn around, although now that he thought about it he should have shooed Tony from the room.

Thankfully he got the message, nodding jerkily before stepping out and closing the door. "I'll wait out here till you're done," he said loudly through the door.

"Okay!" Steve shouted back, burying his face in the mattress and willing the universe to swallow him whole. He should have taken the time to really clean up, but he'd told Tony that it would only be a minute and he felt guilty at the prospect of making him wait after he walked in and had to see that. He ran a hand through his hair nervously before he opened the door. "Sorry about that," he muttered. "What's up?"

"Me and Sharon were wondering if you wanted to get Italian with us tonight."

"You're... inviting me to dinner."

"Yeah."

"With you and your girlfriend."

"Yeah."

Steve chewed on the inside of his cheek. "Thanks but I don't want to crash your date. I'll be fine by myself for the night, you guys can have some fun."

"Steve, we're not inviting you just so you can be a third wheel."

His heart stopped for a second before it continued, and he cursed his ever-hopeful nature. Steve was friends with both of them, that's all Tony meant by it. At least that's what he was trying to convince himself of when Tony continued talking.

"You can still say no obviously, but we meant it as a date. We're both interested in dating you, and we were hoping that you'd feel the same. Of course we were supposed to talk about this over dinner, so Sharon's missing out on this conversation when she wasn't supposed to. Why don't you think about it for a minute, and if you're at all interested, you say yes and we can figure it out over calzones and garlic bread?"

"I'm definitely... interested," Steve said slowly, not anywhere close to admitting that he was in love with both of them and had just masturbated thinking about them.

"Yeah? We're not going to mess with your fantasy person in there?" Tony said, glancing at Steve's room.

He blushed easily, cheeks pinking in embarrassment.

"Sorry," Tony said immediately after. "That was in bad taste. Seven o'clock good for you?" Steve nodded. "Great, we'll see you then."

"Yep. See you." Oh this was a terrible idea, and Steve would probably live to regret it.

***Seven Hours Later***

Steve moaned into the curve of Sharon's thigh as Tony pulled out and thrust back in for the first time. " _Fuck_ ," he breathed, not sure he'd be able to hold his focus enough to get Sharon off while Tony fucked him.

"It's okay," Sharon said, petting a hand through his hair, and Steve was starting to think that maybe he'd said that out loud. "It's okay baby I know how good it feels when Tony's inside you, just enjoy it."

His hands on her hips tightened reflexively, and she let out a shaky breath, reaching a hand down between her legs.

"This is too hot oh my god."

"Are you objectifying me?" Tony asked with a shit eating grin.

"Only as much as you are for me," she responded, working her fingers against her clit and sighing in relief as her eyes got heavier. She gave a little tug to Steve's hair to see if he liked it, and he moaned, so she smiled and did it again.

Steve was like a goddamn piece of art the way he looked when getting fucked, and Sharon couldn't wait to be on the other end of it. She wondered how it would feel if he was inside her right now, and took a deep breath. _One thing at a time_ , she reminded herself. They had plenty of time to try everything under the sun, and god knew that Steve was willing.

"Fuck fuck fuck," Tony chanted, forehead pressed to the sweat slick skin of Steve's back, hips flush with Steve's ass as he grinded against him and came. The bed wasn't rocking anymore, and it felt like a deep breath after being underwater the way the room stilled. "I would apologize for shooting off prematurely," Tony said, voice rough, "but you have _no idea_ what the two of you look like right now, and I'm only a man."

Sharon laughed and stopped touching herself, moving her other hand from Steve's hair down to his neck and rubbing. "I wouldn't worry about it honey, I don't think Steve has any complaints. And if he did, he's about to have even less." She motioned for Tony to pull out, which he did carefully. "C'mon Steve roll over for me babe."

He did so lethargically, face so red and eyes glazed over so it nearly looked like he had a fever-- only fevers never looked so blissed out. Sharon swung a leg over so she was straddling him and reached back to get a hand on his cock, sinking down slowly as she took him in. Steve's breath caught and he scrabbled for purchase at her thighs, but she didn't let that rush her.

"Good lord you're trying to kill me," Tony muttered.

Sharon glanced to the side and caught his eye, giving a sly smirk and winking at him.

"Yep, it's official. I'm a dead man." He settled into the bed to watch though, so evidently he was willing to walk to the gallows.

She put her hands atop Steve's as she started to move, bringing them up to cup her breasts. The angle was good, Steve's cock pressing hard on her clit as she bounced up and down, and it took no time at all before both of them were coming, their coupling an outro to everything they'd done before.

Sharon collapsed on top of him, deciding that her weight was nothing to him so it wouldn't hurt if she cuddled up to him like a personal heater. Tony snuggled closer, also capitalizing on Steve's warmth, and she got a couple hours of sleep in before she had to get up to use the bathroom. When she walked back in, she saw that Tony was now half on top of Steve, who was awake and looking nervous. "Planning on running?" she asked in an undertone so as to not wake up Tony.

Steve's eyes darted to her guiltily. "You're so good together, I don't want to ruin that."

"You're not ruining anything."

"Not yet," he mumbled.

Sharon sighed, crawling into bed again and getting cozy with Steve's other side. And, because she was not above using her breasts to get what she wanted, she may have chosen a position that pressed them up against him. "Even if we go with your assumption that your part in our relationship won't work out, Tony and I have survived a lot together. And you're good Cap, but you're not going to be able to break us up. Me and Tony? We're solid; we're in this for as long as we're both kicking, and your presence isn't going to change that. So if you're worried about things between the two of us, don't."

"You sure?" he asked, glancing at Tony.

"Absolutely. So stop worrying and just enjoy this."


End file.
